Ankle Brachial Index as a Screening Test in Suspected Coronary Artery Disease Patients

Ankle Brachial Index as a Screening Test in Suspected Coronary Artery Disease Patients.




Authors
Tariq Waseem. FCPS Allama Iqbal Medical College/ Jinnah Hospital Lahore.
Naveed Rashid. MBBS Mayo Hospital Lahore.
Abbas Raza. FCPS Allama Iqbal Medical College/ Jinnah Hospital Lahore.


Institute
Departments of Medicine & Cardiology Mayo Hospital Lahore


Correspondence.
Dr. Tariq Waseem
34- Neelum Block Allama Iqbal Town Lahore.
Cell: 0300 8401474
Email: tariqwaseem_59@hotmail.com


Abstract
The resting ankle- brachial index (ABI) is a non-invasive method to assess the patency of lower extremity arterial system and to screen for the presence of peripheral occlusive arterial disease. Diagnostic efficacy of ABI to predict atherosclerosis is well documented and low ABI levels (<>0.9), 2 (1.3%) with mild ABI (0.7- 0.89), and 1 (0.7%) with moderate ABI (0.4- 0.69). In patients with normal ABI 34 (22.7%) patients had normal coronary angiogram, 43 (28.7%) patients had single vessel disease, 33 (22%) patients had two vessels disease, 35 (23.3%) patients had three vessels disease, and 2 (1.3%) patients had four vessel disease. In patients with mild ABI (0.7- 0.89) there was 1(0.7%) patient who had single vessel disease, and 1 (0.7%) patient with four vessel disease. In the moderate ABI category (0.4 – 0.69) there was 1 (0.7%) patient of two vessel disease.

Conclusion: Ninety eight percent of the studied population with otherwise symptomatic coronary artery disease had normal ABI. On the other hand 77% of patients with normal ABI had abnormalities on coronary angiogram. ABI lacks the sensitivity to screen atheromatous CAD and cannot be recommended as such.
Key Words: Ankle brachial index, coronary artery disease, coronary angiography.


Introduction
Patients already having evidence of atheromatous vascular disease are at higher risk of another vascular event and can be offered a variety of primary and secondary preventive measures to improve their outcome.1 Patients with peripheral arterial disease (PAD) have a high prevalence of coexistent coronary artery disease (CAD).2 They are at triple the risk of all cause morality and at more than six times the risk of death from coronary artery disease as compared to those without the disease.3 Under-diagnosis of peripheral arterial disease in primary care practice may be a barrier to effective secondary prevention of high ischaemic cardiovascular risk associated with peripheral arterial disease.4
Ankle brachial pressure index (ABI) being simple and easy to perform technique should be included early in the clinical consideration of patients with symptoms suggesting coronary artery disease.3,5 Ankle brachial index is the ratio of ankle and brachial systolic pressures measured with the help of a hand held Doppler. Normal value of ABI is >0.9 and <1.406. or =" 0.90)">0.9.14 These data demonstrate that low ABI levels, particularly those of <0.9,>0.9 (normal), 2 (1.3%) patients of ABI of 0.7-0.89 (mild), 1 (0.7%) patient of ABI of 0.4-0.69 (moderate) and no patients of severe ABI (Table 5).
In the CAD findings, there were 34 (22.7%) normal finding, 44 (29.3%) patients of single vessel disease, 34 (22.7%) patients of two vessels disease, 35 (23.3%) patients of three vessels disease and 3 (2%) patients of four vessels disease (Table 6).
In the relationship between ABI and extent of coronary artery disease, in the normal ABI (>0.9) there were 34 (22.7%) patients of normal CAD, 43 (28.7%) patients of single vessel disease, 33 (22%) patients of two-vessel disease, 35 (23.3%) patients of three vessels disease and 2 (1.3%) patients of four vessel disease. In the mild ABI (0.7-0.89) there was 1 (0.7%) patient of single vessel disease and 1 (0.7%) patients of four vessels disease. In the moderate ABI (0.4-0.69) there was 1 (0.7%) patient of two vessels disease (Table 7).



Table 1
Distribution of patients by Age
(n=150)

Age (Years) No. Percentage
<50>50 95 63.3
Mean±SD 51.23±10.23

Key:
SD Standard deviation
<> Equal to or more than



Table 2
Distribution of patients by sex
(n=150)

Sex No. Percentage
Male 118 78.7
Female 32 21.3
Total 150 100.0




Table 3
Distribution of patients by symptoms
(n=150)

Symptoms No. Percentage
Dyspnea 20 13.3
Chest pain 112 74.7
Palpitation 3 2.0
Arm pain 5 3.3
Epigastric pain 4 2.7
Chest heaviness 6 4.0





Table 4
Frequency of Major CVD risk factors
(n=150)

Risk Factor No. Percentage
Smoking 66 44.0
Hypertension 63 42.0
Diabetes 37 24.7
Dyslipidemia 9 6.0




Table 5
Distribution of patients by ABI
(n=150)

ABI No. Percentage
>0.9 147 98.0
0.7-0.89 2 1.3
0.4-0.69 1 0.7
<0.4>0.9 Normal
0.7-0.89 Mild
0.4-0.69 Moderate
<0.4 n="150)" n="150)">0.9 34 43 33 35 2 147
0.7-0.89 0 1 0 0 1 2
0.4-0.69 0 0 1 0 0 1
<0.4>0.9), 1.3% patients of mild ABI (0.7-0.89), 0.7% patient of moderate ABI (0.4-0.69) and no patient of severe ABI (<0.4).>0.9) patients, 22.7% patients had normal angiography, 28.7% patients had single vessel disease, 22% patients had two vessel disease, 23.3% patients had three vessel disease and 1.3% patients had four vessel disease. In the mild ABI (0.7-0.89), 0.7% patient has single vessel disease and 0.7% patient had four-vessel disease. In the moderate ABI (0.4-0.69) 0.7% patient had two-vessel disease.
The ABI is a simple, noninvasive, and reliable test that can be complementary to conventional vascular risk factor profiles to identify individuals from the general population who are at high risk of developing cardiovascular disease and could benefit from preventive measures.23 After adjusting for conventional cardiovascular risk factors and prevalent cardiovascular disease, a low ABI (<0.90) is an independent predictor of cardiovascular risk. A low ABI is also highly specific (88%-93%) for predicting future cardiovascular events (ie, a low ABI helps to "rule in" a high-risk patient), with likelihood ratios of about 2.5 for coronary heart disease, 2.4 for stroke, and 5.6 for cardiovascular death. However, because the sensitivity of a low ABI to predict future cardiovascular outcomes is low (i.e., a normal ABI does not "rule out" a high-risk patient), the ABI lacks usefulness as a screening test for CAD in the general population. Further clarification of the role of ABI awaits evaluation of its incremental predictive value over conventional methods of risk assessment in patients who may be at increased risk of cardiovascular disease.23 Its optimal application may be as part of the vascular risk assessment among selected individuals without established vascular disease but older than 70 years or among those who are aged 50 to 69 years and have 1 or more cardiovascular risk factors i.e., elevated serum cholesterol level, hypertension, dysglycemia, tobacco exposure, or a family history of atherosclerotic disease.24
Our patients were younger with a mean age of 51 years when compared with those of Doobay and Anand23 who were 50-69 years old and had one or more cardiovascular risk factors. Perhaps this is the reason of finding a lower frequency of low ABI and hence lower PAD in our patients who otherwise comprised of symptomatic patients having significant abnormalities on coronary angiography. Despite its documented usefulness to predict peripheral vascular disease ABI remains insensitive to predict CAD in younger patients. Peripheral vascular disease may be lagging behind CAD by a decade to become manifest in our patients.

Conclusion
ABI cannot be recommended as a screening tool for atheromatous CAD in our population. 98% the studied population with otherwise symptomatic coronary artery disease had normal ABI. On the other hand 77% of patients with normal ABI had abnormalities on coronary angiogram. A low ABI helps to "rule in" a high-risk patient but a normal ABI does not "rule out" a high-risk patient. The ABI lacks usefulness as a screening test for CAD in the general population.

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